1. Field of this Invention
This invention relates to a process for the production of 3,5-dialkylpyridines.
2. Prior Art
3,5-dialkylpyridines are important intermediate products in the chemical industry, for example, in the production of plant preservatives or dinicotinic acid. Various processes for the production of 3,5-dialkylpyridines are known.
3,5-dialkylpyridines have been produced in a gas phase reaction from formaldehyde, ammonia and an aliphatic aldehyde of the formula R--CH.sub.2 --CHO (see French Patent No. 1,332,908). Thus, from formaldehyde, n-butyraldehyde and ammonia, 3,5-diethylpyridine was obtained at 400.degree. C. on an aluminum silicate catalyst impregnated with lead fluoride. The yield corresponded to a conversion of 50 percent. Analogously 3,5-dimethylpyridine was obtained from formaldehyde, propionaldehyde and ammonia solution. Such a process has not attained any technical importance. The necessity of having to always regenerate the catalyst in oxygen or in a stream of air is a serious disadvantage. Due to the required high temperatures, a pitchlike material and its decomposition products are formed--they cause coking of the apparatus and catalyst and make the separation of the desired 3,5-dialkylpyridine difficult.
According to German OS No. 2,123,965 a precondensate of formaldehyde and an aldehyde R--CH.sub.2 --CHO is formed in the first step of a two-step fluid phase process. Subsequently the precondensate is transformed into 3,5-dialkylpyridine in a second step with ammonia and/or ammonium salts at 200.degree. to 300.degree. C. over 8 to 10 hours. The yields lie between 11 and 46 percent. The disadvantage of such a process is that it has two steps and requires long reaction times.